1. Field of the Invention
This invention relates to methods and apparatus for making an orthodontic appliance that is comprised of a clear polymeric material.
2. Description of the Related Art
Orthodontic treatment involves movement of misaligned or crooked teeth to improved positions. Orthodontic treatment can greatly enhance the patient's facial appearance, especially in areas near the front of the patient's oral cavity. In certain instances, orthodontic treatment can also improve the occlusion in such a manner that opposing teeth will function better with each other during mastication.
One type of common orthodontic treatment includes the use of a set of brackets, each of which is affixed to a respective tooth in the patient's mouth. A resilient arch-shaped wire is placed into a slot of each bracket and functions as a track to guide movement of the bracket and hence the associated tooth to desired positions. Ends of the wire are often retained in channels of small devices known as buccal tubes that are secured to the patient's molar teeth.
Another type of orthodontic treatment involves the use of resilient polymeric trays that fit over the teeth of the patient's dental arches. These trays, also known as aligners, alignment shells and polymeric appliances, are provided in a series and are intended to be worn in succession in order to gradually move the teeth in incremental steps toward a desired target arrangement. Some types of polymeric appliances have a row of tooth-shaped cavities for receiving each tooth of the patient's dental arch, and the cavities are oriented in slightly different positions from one appliance to the next in order to incrementally urge each tooth toward its desired target position by virtue of the resilient properties of the polymeric material.
A variety of methods have been proposed in the past for manufacturing polymeric appliances. According to one known method, a digital data file is obtained that represents the patient's upper and lower dental arches at the beginning of treatment. This data file is then analyzed to identify subsets of data, each of which represents one of the patient's teeth. Next, a technician then uses a computer input device (such as a mouse or keyboard) to virtually reposition the maloccluded teeth and move individual teeth on a computer screen relative to each other into desired target positions. The target positions are then reviewed and approved by a treating professional, such as an orthodontist that is located remotely from the technician.
Once the proposed tooth arrangement has been approved, the data representing the initial tooth positions and the data representing the target tooth positions are then used to determine intended intermediate positions of the teeth as the teeth move from initial to target positions. As one example, data representing the differences in tooth positions between the initial tooth arrangement and the target tooth arrangement may be interpolated in order to obtain a series of twenty intermediate positions of the teeth. The data representing those intermediate tooth positions is then stored in memory and subsequently used to make models of the dental arches for each intermediate tooth arrangement.
For example, a data set representing the teeth in a desired target arrangement and twenty data sets representing the teeth in twenty different intermediate arrangements may be used to manufacture a series of twenty-one physical, positive dental arch models for each dental arch using rapid prototyping methods such as stereolithography. Subsequently, a sheet of polymeric material is placed over each of the arch models and formed under heat, pressure and/or vacuum to conform to the model teeth of each model arch. The formed sheet is cleaned and trimmed as needed and the resulting arch-shaped appliance is shipped along with the remaining appliances to the treating professional. The patient is then instructed to wear each appliance over its intended dental arch in sequence for a period of, for example, two or four weeks, after which the used appliances are discarded and the next two appliances in the series for the upper and lower dental arches are to be worn.